This invention concerns a push switch with a push rod which encounters during its movement stroke, a pressure point (or resistance point), a contact-making point, and return pressure caused by spring action.
Such push switches are disclosed in German Gebrauchsmuster 81 14 214.5, German Offenlegungsschrift 35 20 848 A1, European Patent 0 074 004 A2, European Patent 0 123 818 A1, and European Patent 0 515 943 A2. In these publications spring elements are respectively provided for each of the functions: pressure point creation, contact making, and return force. Fabrication and mounting expenses are correspondingly great. Further difficulties result where a switching stroke of a push rod is small if it must be assured that, during such a stroke, the pressure point is encountered before the switching point.
Such a push switch is also disclosed in German Patent DE 36 22 962 A1. With this switch, a clearly perceptible movement is supposedly achieved for a small stroke, for example a stroke in a range of 1 mm to 3 mm, with the pressure point lying before the switching point. Such switches are required, for example, for motor vehicle electrical circuits.
In the push switch of German Patent DE 36 22 962 A1 an end winding of a spiral shaped return spring, with inwardly directed deformed portions which cooperate with a sloped engaging edge of a push rod, is provided for creating a pressure point. A contact-making, or closing, is brought about by a contact spring assembly which is independent thereof. The structural arrangement of the contact spring assembly and the push rod is tolerance sensitive in view of the short stroke and a required switch path. The spiral shaped return spring, with its inwardly directed deformed portions which provide radial spring action, is difficult to dimension. Further, friction is caused between the above mentioned portions and the push rod after the pressure point has been overcome.
Additionally, a contact pressure cannot be reinforced by the push rod.
Thus, it is an object of this invention to provide a push switch of the type mentioned above which, with an uncomplicated structure and a short stroke, provides a reliable contact movement once the pressure point has been overcome.